1. Field of the Invention
This invention relates to a method and an apparatus for producing a laminated object in which a deposited layer, constituted by depositing a material capable of forming a solid layer, is irradiated with a laser beam to form a solid layer and in which the solid layers are piled to constitute a three-dimensional laminated object.
2. Description of the Related Art
A method for producing a laminated object has been developed recently. This method is disclosed in Japanese Unexamined Patent Publication (KOKAI) No.3-183,530, U.S. Pat. No. 4,247,508, and others. This method alternatively repeats a depositing step and an irradiating step. In the depositing step, grains are deposited to constitute a deposited layer. In the irradiating step, the deposited layer is irradiated with a laser beam to constitute a solid layer and a large number of solid layers are piled to produce a three-dimensional laminated object. This method, as appreciated in FIG. 26, has a problem that convex portions 301, having a diameter corresponding a spot diameter "D" of the laser beam substantially, remain at an edge of a solid layer 300. An increase of the spot diameter "D" generates that the convex portions 301 are large to deteriorate accuracy at an edge of the solid layer 300, thereby deteriorating accuracy at an edge of the three-dimensional laminated object. For realizing excellent accuracy at the edge of the three-dimensional laminated object, it is required that the spot diameter "D" is extremely small. For instance, the spot diameter "D" is as minute as 0.2 mm. This case improves accuracy at the edge of the three-dimensional laminated object; however, this case increases a required irradiation time considerably and causes a disadvantage in high speed production and production ability. This method, therefore, is not always fitted to mass production but is fitted to production of experimental articles.
For improving production ability in this method, it is a preferable mode to increase laser output. This mode, however, excessively increases irradiation energy with respect to the deposited layer per unit area. Thus, this mode requires that scanning speed and on- off control speed of the laser beam are high for preventing overheat. Also, high speed in scanning speed exhibits a limit at a present situation; so, improving production ability is very hard in this method.
For improving production ability, it is another preferable mode to use a spurious laser beam generated by means of a segment mirror method, a kalaid scope method, and the like. This mode, however, trends to cause energy eneveness of the laser beam; so, this mode is not always fitted in producing a three-dimensional laminated object.
Also, the above-mentioned laminated object producing method is disclosed in National Unexamined Patent Publication of the Translated Version of PCT Application (KOHYO) No. 8-502,703. This method, as appreciated in FIG. 27, uses a raking member 400 coming into contact with the deposited layer 300. A top end of the raking member 400 rakes a surface of the deposited layer 300 in the depositing step to average a thickness of the deposited layer 300.
Another method is disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 3-183,530. This method, as appreciated in FIG. 28, uses a rotating roller 500 coming into contact with the deposited layer 300. The rotating roller 500 levels a surface of the deposited layer 300 in a depositing step to average a thickness of the deposited layer 300. In accordance with such publication method, the raking member 400 and the rotating roller 500 always comes into contact with the deposited layer 300.
In accordance with such publication methods, since the deposited portions is raked to be levelled by using the raking member 400 or by using the rotating roller 500, a frictional force is easily applied to a lower layer formed under the deposited layer 300, thereby slipping or damaging the lower layer by a shear stress. This deteriorates accuracy of the laminated object. As result, in such publication methods, it is required that a depositing speed of a depositing apparatus is set at a low speed or an ultra low speed during depositing step. Also, since a limit exists in increasing the depositing speed and the forming speed, such publication methods may cause insufficient production ability, in particular, because of a large number of the layers. So, the method for the three-dimensional laminated object isn't fittable to mass production although it is fittable to experimental articles.